This invention relates generally to tunneling machines, and more particularly to tunneling machines having a rotary boring or cutting head for boring passages through hard rock and minerals.
The digging of a tunnel through soft material, such as clay and soft rock or only partially consolidated materials, has long been done by machines having a rotary cutting head having cutters which scrape and dig away at the material, which is then collected and removed rearwardly from the tunnel. However, when such machines are used against harder materials, and particularly very hard igneous and metamorphic rocks, such scraping type cutters cannot be used, and it is necessary to employ percussive-type roller cutters which chip away small fragments from the mass of rock by impact. The use of such cutters has long been known for drilling wells and other relatively small diameter holes, but efforts to adapt such cutters to larger machines for use in drilling tunnels have met with considerable difficulty because of the necessary forces involved and the shock loads encountered.
A reliable and proven machine has been developed for cutting hard rock at a fast enough cutting rate to make it competitive with prior tunneling methods. That machine is set forth in U.S. Pat. No. 3,383,138. According to that patent, a fixed supporting frame is anchored in the tunnel by two axially spaced sets of projecting arms, each set of which has four arms equidistantly spaced and actuated by hydraulic cylinders to position the frame without regard to the weight of the machine. A movable frame is carried centrally within the supporting frame by sets of torque arms at each end, which both support the moving frame and transmit the reaction torque from the moving frame to the supporting frame. A cutter head is mounted in bearings at the front end of the moving frame and carries a cutter plate having a number of roller cutters mounted thereon. A drive shaft extends the length of the moving frame to project beyond the rear of the supporting frame where the shaft is driven by a plurality of motors which drive an encircling ring gear. Hydraulic cylinders acting between the supporting frame and the cutter head apply the force directly to the bearing supporting the cutter head to cause the moving frame to move relative to the supporting frame. After the moving frame is moved through its full range of movement, a jack is lowered at the rear end to support the moving frame by the jack and the cutter head to allow the supporting frame to have the arms retracted and moved forward to the next position, where the supporting frame is again anchored to allow the cutting movement to continue.
Tunneling machines according to the foregoing patent are adapted to bore tunnels having diameters from eight to 30 feet and more. Those machines are not entirely suited for drilling tunnels of diameters smaller than eight feet. Merely scaling down the machine shown in the foregoing patent reduces structural and hydraulic capabilities of the machine. Limiting factors as to the diametrical size of the tunneling machine according to U.S. Pat. No. 3,383,138 are the torque arms, which travel in a radial direction, the radially offset placement of the hydraulic cylinders, which drive the cutter head forwardly, and the radially offset placement of the motors, which are employed to drive the ring gear associated with the cutter head drive shaft.